This invention relates to a shape sawing apparatus wherein a curved log or cant (hereafter collectively referred to as a cant) is cut along curved lines to maximize the production of lumber therefrom and more particularly it relates to the apparatus that manipulates the saws for obtaining the curved cut.
The benefit of producing lumber from curved cants by cutting the cants along a curved cutting line, as dictated by the configuration of the cants, is well known to the industry. One way of accomplishing such curved cutting is by feeding the cants in a linear path to the saws and manipulating the saws rotatively and laterally to follow a projected curved cutting line through the cant. It is this cutting process to which the present invention is directed.
The required movements of the saw, i.e., laterally and rotatively, has heretofore required a carriage for the saw that is movably mounted on a base member, e.g., rotatively, with that base member movably mounted, e.g., laterally, on a second but fixed base member. The provision of such dual movement on dual base members is both complex and expensive. It is an objective of this invention to produce the desired dual movements on a single fixed base member.
Determining the optimum positioning of the saw is also an objective of this invention. The saw that is used for cutting is a bank of planar circular saw blades. The portion of the circular periphery of the rotating saw blade that cuts the cant is angled upwardly and rearwardly and is substantially a straight inclined cutting edge. FIG. 6 illustrates the cutting of a cant by a circular saw blade and the portion referred to as the inclined cutting edge portion is between points 104 and 102. This cutting edge portion has both length and height and the length portion is straight whereas the projected kerf being cut by the blade is curved. Thus the blade is constantly repositioned to follow the kerf and because the blade is straight and the kerf is curved, only a single point on the cutting edge portion of the blade can be truly on the projected kerf. This point is referred to as the point of tangency. The effect on the lumber being cut is that the sawn side of an outside or face board is not flat and thus not parallel to the chipped outer flat side produced by a chipper. (Chipper cutting occurs along a vertical line and thus produces a flat face regardless of alignment.)
In known prior devices, the closely adjacent but necessarily spaced apart saw and chipper are commonly mounted for simultaneous positioning, laterally and pivotally. Any change to the assembly affects both the chipper and the saw blade, and the point of tangency (determined by the pivot point for the assembly) is established rearward of the chipper and forward of the saw. Neither the chipper or the cutting blade is precisely positioned on the projected kerf and the sawn side is not only not flat but it is non-symmetrical which can affect the grading of the lumber.
The preferred embodiment of the present invention has a carriage that carries the saw, the carriage being movably mounted both rotatively and laterally on a single fixed base member. The base member is a large plate having an upper flat surface including a lateral slot near its center. The carriage has depending multiple strategically positioned pads with flat bottoms that engage the flat surface of the base member and which support the weight of the saw.
Depending from the center of the carriage is a post that fits into the slot of the base and defines the pivotal axis. Hydraulic cylinders strategically positioned between the support and base move the carriage both laterally and pivotally as permitted by the sliding connection of the post in the lateral slot. The pads simply slide on the flat plate. The materials of the pad and flat surface of the plate are selected to minimize friction. A pliable skirt surrounding each pad provides a seal to inhibit contaminants, and an inlet to the center of each pad injects oil and air between the engaging surfaces. The oil lubricates the surface (reducing friction) and the air (depending on pressure) provides a partial air cushion between the pads and surface and/or an air curtain at the rim of the pad to assist the skirt in preventing contamination between the engaging surfaces. The pads are able to slide in any direction on the base member but are confined by the limited linear movement of the carriage post in the slot of the base member and rotatively by the reach of the hydraulic cylinders. A computer is programmed to control the cylinders for achieving the desired position of the saw or saw blades carried by the carriage.
To optimize the sawed face of the lumber, a point of tangency is established behind the leading point of the cutting edge portion and in front of the trailing point of the cutting edge portion. The preferred position is about mid-way between these points. This establishment of the point of tangency for the saw blades is accomplished by strategically positioning (laterally) the pivot for the carriage and also the positioning (pivotally) of the saw along a radial line that passes through the desired points of tangency for each of the saw blades. The computer controls the pivoting of the saws about the pivotal axis to align the points of tangency with the radius of the kerf""s curvature.
The cutting done by each cutting edge portion both before and after this point of tangency will be offset from the computed or projected kerf. However, both before and after the mid-point the offset is in the same direction, i.e., as viewed in plan view the entry and exit points will both be at the convex side of the kerf. At any vertical cross section the face of the board, top to bottom, is slightly curved being convex on one side of the cut and concave on the other side of the cut. The thickness of the boards at the top and bottom edges will be essentially the same and the middle slightly less or greater assuming the cut board is a face board having a flat exterior face, e.g., produced by a chipper.
In the prior method with the pivotal axis in front of the saw, the cut starts at an offset position from the cutting line and continues to increase in that same offset direction and thus produces an angled face top to bottom (that is also slightly curved) with the top and bottom edges of the board having different thickness dimensions.
Recognition of the effect involved when a circular, planar blade is cutting a curved kerf enables the optimum placement of the pivot axis and thus the point of tangency as described above. The boards that are cut satisfy industry standards where they may not satisfy those same standards using prior cutting methods.
The above improvements will be more fully appreciated and understood upon reference to the following detailed description and drawings referred to therein.